Constitutive Expression of Chimeric Transcription Factors Enables Cellulase Synthesis under Non-Inducing Conditions in Penicillium oxalicum.

Industrial production of cellulase by filamentous fungi is largely dependent on cellulose, which serves as a natural inducer of cellulase expression. However, insoluble cellulose is unfavorable to submerged fermentation and thus limits the production level of cellulase. The possibility of cellulase production under non-inducing conditions is explored in Penicillium oxalicum by overexpressing two chimeric transcription factors. The chimeric transcription factors contain the DNA binding domain of cellulase transcriptional activator ClrB linked to the C-terminal sequences of XlnRA871V , a constitutively active mutant of hemicellulase transcriptional activator. The obtained recombinant mutants exhibited dramatically improved basal production of cellulase, which was not observed with the overexpression of intact ClrB. When cultivated in a complex cellulosic medium, one of these mutants, OE-CXC -S-1, displayed a 7.3-fold increase in cellulase production (2.8 U mL-1 ) relative to the parent strain. The results demonstrate that the dependence of cellulase synthesis on cellulose could be reduced by the overexpression of artificially designed chimeric transcription factors, and offers a potential strategy to engineer fungal strains for improving cellulase production.